Music Tech - February 2011
MTMReviews Focusrite ISA428 MkII
Focusrite’s ISA428 MkII is a high-quality four-channel microphone preamp. John Pickford puts it through its paces.
ISA428 MkII Manufacturer Focusrite Price £1,439 Contact Focusrite 01494 462246 Web www.focusrite.com
It can be all too easy to underestimate the importance of a good-quality mic preamp in the recording chain. The job of amplifying the tiny signal from a microphone into something usable is difficult to do well, but crucial in order to maintain fidelity. If you have a collection of good-quality mics, they deserve better than to be plugged into a budget-price mixing desk in which the preamps are often mediocre at best. Focusrite’s MkII version of the ISA428 provides four channels of transformerbased preamplification, designed to bring out the best in any microphone. Visually, the unit is sensibly laid out and thoroughly modern – no seductively backlit VU meters or funky retro chic going on here.
Around the back, each channel has an XLR mic input and channel output sandwiching three 1/4-inch jack sockets. One of these is a line-level input, the other two are insert send and return, allowing for an external unit to be placed within the signal chain,
KeyFeatures ●4channels of preamplification ● Insert send/
return per channel ●Line-/mic-level inputs per channel ●Up to 60dB gain
MethodSpot One of the beauties of having four channels of mic preamplification is that it enables you to really hear the different tonal characteristics of your mics. When recording a vocal, for example, set up four different mics and experiment to see which one is best suited to that particular voice. You’d be amazed at how often an inexpensive dynamic such as a Shure SM58 can be a better match than a costly condenser from the likes of Neumann or AKG (remember to listen to each channel in isolation, though).
bypassing Focusrite’s high-pass filter. There are also four XLR ADC inputs, but these are for use in conjunction with the eight-channel digital output option, not supplied for review. Four jack sockets on the front of the unit enable guitars and basses to be plugged in without the need for an external DI box and these inputs will also accept the highimpedance output of vintage synths.
In control The front panel features three rotary pots per channel. The largest controls input gain, providing gain in 10dB steps from 0dB to +60dB. The pot moves through three steps, which means a button (marked 30–60) must be pressed to employ higher amounts of gain. Below the gain control are two smaller pots. The Trim control provides additional gain of up to 20dB. This pot is continuously variable, allowing for fine-tuning of gain settings; it’s recommended that some trim gain is applied before using the 10dB stepped pot so that gain may be gently added or taken away later. The third pot controls the unit’s high-pass filter, providing an 18dB/octave roll-off which is variable within the range of 16Hz to 420Hz.
Pressing one of the five buttons to the left of each channel block activates the filter, while the other four buttons switch in the insert, enable the second range of gain, invert phase and provide +48V phantom power for condenser microphones respectively. These buttons illuminate when active.
switch in the insert, enable the second range of gain, invert phase and provide +48V phantom power for condenser microphones respectively. These buttons illuminate when active.
Two further buttons sit to the right
Two further buttons sit to the right of the input gain control. The Input button selects each of the three inputs – mic, line and instrument – and the corresponding LED indicates which source is active. As each channel has independent switching, a variety of microphone, instrument and line inputs can be implemented across the four channels at the same time. The remaining button (marked Z in) selects one of four impedance values – 600 ohms, 1k4 ohms, 2k4 ohms and 6k8 ohms – enabling precise control over the synergy between preamplifier and microphone. The 1k4 setting is designated ISA 110 on the front panel as it is a faithful re-creation of Focusrite’s original ISA 110 mic pre. Output levels are displayed by a row of LEDs to the right of the front panel.
We began our listening test by connecting our FET version of the Neumann U47 microphone. On spoken word, the first thing that struck us was just how even-handed and natural the Focusrite sounded from top to bottom. The voice sounded real and convincing, not overblown and glorified nor thin and constrained. Some mic preamps, especially those that employ valves in the design, have a very obvious sonic character that inspires phrases such as ‘creamy and velvet-smooth’ or ‘sparkling top end’. The ISA428 does not invoke those images but that’s not to say that it lacks character – it doesn’t, it simply gets on with the job of amplifying the signal and allowing the microphone to display its own character.
Trying to pin down the sound of the Focusrite, we would say that it is full-bodied and warm at the bottom end without sounding overly rich or gloopy. The broad mid band is open and transparent with no particular emphasis on any one area of the
106 | February 2011 magazine